Tighten up you mount screws! A100/lenses.

This has also been posted on dPreview:

When testing the 16-80mm I found that mount tolerances - amount of slack or rotation - vary greatly from camera to camera. The 16-80mm on my A100 was about the loosest overall fit mount to mount.

Further investigating, I dismantled a broken 7000 to examine the mount. As a result, I took my precision screwdriver (exact fit, no risking messing up these small crosshead screws) and attacked the Alpha 100. All of the lens mount screws took between 1/4 and 1/2 a turn of tightening up to get to a normal, hand-judged tightness. Whether this is a result of six months of use I don't know, but I then checked our 5D and 7D. 5D - about half the slack of the A100; 7D - most use - two of six screws needed 1/4 turn, rest very firm.

I also checked the CZ 16-80mm. All mount screws accepted an easy 1/4 turn of additional tightening. Our well-used 100-300mm APO - rock solid, no tightening possible. 24-105mm - about 1/8th of a turn on all four screws.

After adjusting all the mounts - bringing the six body mount screws and four lens mount screws up to a firm, safe hand torque using a screwdriver with a 3/4-1" size contoured handle, not a thin handled jeweller's screwdriver - fit was much improved. The sloppy fit of the A100/16-80mm was almost gone (small degree of play remained, normal). The 7D with its two slightly loose screws tightened was very tight on our 100-300mm, some resistance in mounting, but the result dead firm with zero slop.

The lenses feel better on the cameras all round, and I now intend to tighten all lens mounts, and check the bodies periodically. I could swear the adjustment has also cured some front focus issues with ultra-wide lenses, but only field use with the 16-80 and 11-18 will tell me. I guess that if there was so much slack on the body mount screws, and so much on the lens, this could add up to a few microns, enough to shift focus visibly on such short focal lengths.

It had not occurred to me before this that factory tolerances or torque settings for tightening up screws might be responsible for sample variation, or deterioriation in use. I'm surprised I was so easily able to tighten important fixings on both body and lenses.
David
photoclubalpha.com

I have just checked all my lenses from 70-210 beercan through 500mm mirror, both macros, 100 soft, 28 f2, KM 28-75 and 17-35, 50mm 1.4 etc. Not one of these older lenses had the same lack of tightness on the mount screws as the Alpha 100 body or the CZ 16-80mm lens. In fact, it would have been risking damaging the screws to try to tighten them. A couple had one screw able to take a tiny shift, maybe 1/16th or 1/32nd of a turn. And some of these are 20 years old. Also very solid - fully tight and firm - were the Sony and KM 18-70mm kit lens mounts, despite being plastic.

After realising just how solid the screws were in the older kit I returned again to the A100 and found that I the bottom-most mount screw could take a further 1/4 turn to be equally tight, and one other screw, about 1/8th. I now have them all as tight as 'vintage' assembly. Also, the 16-80mm checked again took a small additional tightening up on a couple of the screws. Now feels as firm on all four as my 70-210mm.

This means some of the screws have taken at least half a turn and were very slack indeed.

David

Brettania -

Any small electronics screwdriver set will work just fine. A few examples of sets that would work:

http://www.radioshack.com/product/index.jsp?productId=2062783
http://www.radioshack.com/product/index.jsp?productId=2062774
http://www.radioshack.com/product/index.jsp?productId=2062773

Pic of screwdriver I have been using - much easier to judge tightness but you could wrap a load of stuff round a thin handle to make it more responsive.

http://www.iconpublications.com/screwdriverkit.jpg

David

Great discovery. Thanks for sharing.

After reading this thread yesterday I went and checked the mount screws on my A100, Sigma 17-70, Tokina 80-200 (gold ring version), and Sony 18-70 kit lens.

The mount screws and the two screws on the front plate as well as the small screw on the bottom on the front plate all took at least 1/4 of a turn of tightening on my A100. One of the mount screws took almost a full turn to of tightening!!!

The screws on my Sigma 17-70 accepted a bit of tightening, about 1/8th of a turn each. In contrast, the Sony kit lens as well as the Tokina 80-200 (I had it for about a month, but I think its about a decade old) didnt take any tightening.

Thanks David :)

if its possible to prove this tolerances are enough to shift focus, this little tip can turn into a very serious thing..

after writing this, i realised that it cant cause BF/FF, because AF works TTL the effect would be offset. However the effect would go on like a micron sized extension tube. Would it harm infinity focus? no way..

but still it made me feel bad.. a camera is ought to be well screwed together!